Fuel injection pumps for internal combustion engines



May 5, 1959 s. M. BUTLER 2,884,919

FUEL INJECTION PUMPS FOR INTERNAL COMBUSTION ENGINES Filed July 31, 1957I 2 Sheets+Sheet 1 ENGINE SUPERCHARGER AIR PRESSURE COMPRESSED F AIRRESEVOIR IN l/ENTO Q BY f ATTORNEY y 5, 1959 s. M; BUTLER 2,884,919

FUEL INJECTION PUMPS FOR INTERNAL COMBUSTION ENGINES Filed July s1,195'! v 7 2 Sheets-Sheet 2 INVENTOR BY ATTORNEY FUEL..I NJECTIONP.UMPSFOR IN'IERNAL COM U T N EN NES :Stanley M. Butler, Hounslow, England,assignor to Alan Muntz & Company Limited, ;Hounslow, Middlesex, EnglandApplication July 31,1951, Serial No. 675,436 ,Claimspriority,applicationGreat Britain July 31, 1956 s laim to. 123-1139.)

The present invention relates to fuel injection pumps for internalcombustion .engines employing high compression pressures. Such enginesmay vbe highly supercharged.crankshaftor freepiStonengines. By a free-;piston engineinthisspecification and in the appended lclaims is meanteither a free-piston gas generator or a ,free-piston gas-compressor. .Inthese free-piston ,en-

gines an engine piston operating in an engine cylinder is.directlyconnected-to a compressorpistonoperating in a :compressorcylinder, ,the .engine operates on the two- .stroke Diesel cycle, andenergy accumulated 'by com- -pre,ssio n of air in a cushion on one sideof the compressor derived wholly from the exhaust ports of ,the engine.

.In a gas-compressor the air compressed in the compressorcylinder orcylinders is delivered directly to the prime-mover without first passingthrough the engine.

It is well known to use with conventional crankshaft :Diesel enginesoperating with normal compression pressures what is known as agas-operated fuel injection pump, that is -,to say a fuel injection pumpwhich is driven by gas pressure from the :Diesel cylinder. Thus athegas/pressure in the diesel cylinder may be applied to the-pistonofthefuel pump directly, and the fuel pres- ,sure is then proportionalto the gas pressure. As the 'gas 'pressure risestduring the compressionstroke the fuel pressure-rises until it :reaches the pressure to whichthe injectors are set. The fuel valves then open and the fuel isinjected at a steadily increasing pressure, .until the ,wholeof the fuelinthe pump cylinder has been delivered. The quantity of fuel iscontrolled in the usual way by means of a spill port in the pump, whichis closed at a pointin the stroke of the plunger at which .the requiredquantity of fuel is trapped in the pump barrel.

With .the injectors set at a panticular pressure, a pump working in thisway will-theoretical1y start inject- ;ing ata point in the compressionstroke at which the compression pressure reaches a value correspondingto the setting pressure of thejinjectors. The ratio-of areas of th g p son an th p mp p un i usu y a ,about l :1 for a conventional dieselengine. Thismeans, for example, that with the injectors set at 1,800.p.s.i. the start of injection will occur when the compression pressurereaches 180 psi, and if the maximum cylinder pressure is 1,000 p.s.i.,the maximum fuel pressure will not exceed 10,000 p.s.i. Moreover, thismaximum pressure will only be reached if the injection period is con-,tinued until the maximum cylinder pressure is reached atabdut 'theinner dead centre.

United States Patent C) The design of a gas-operatedfuel-injeetionpump'for a high compression ,pressure engine such as a freepiston enginepresents ditficulties for the following rea sons. Firstly, the injectorpressure setting is considerably higher than .in a conventional dieselengine, for

instance it may be about 2,800 p.s.i,, because of-the relatively highmaximum cylinder pressures that are used in free-piston engines,particularly at full load. Secondly, the compressionpressures-oceurringat thetime-when injection is required to start mayvary from about 1150 p.s.i.g. when idling to about .250 ;p.s.i.g. atfull ;l oa d.

These peculiarities of a high compression pressure engine give rise tothe following objections:

Firstly a simple pump with a-ratio of'gas piston area to pump plungerareaof 10:1,,requiring a gas pressure of 280 p.s.i. to openthefuel-valves in the injectorswould give too late an injection underall conditions, and secondly, if the area ratio were chosen to give thecorrect injection timing at full load, it would still be much too latewhenidling.

There is also the objection of t-he lateness -of-the; in-

jection at all loads, and means mustbe provided to overcome thisobjection.

In theory, this objection could be overcome by sufficiently increasingthe .ratio of the area of the gas piston to the area of the pumpplunger. This, however, results in maximum fuel line pressures which aretoo high for many purposes. For example, with a ratioof 18 .or 2011which mightbe required, and a maximum cylinderrpressure of 1,800 p.s.i.,the maximum :fuel line pressure would be 33,000 to 36,000 psi Thepresent invention has for its main object ,-to provide a gas-operatedfuel-injection system for highcom- 'pression pressure engines in whichexcessive fuel line pressures are avoided.

According tothe main feature of the invention, therefore, in agas-operated fuel-injection system for a high compression pressureengine there is provided an accumulator adapted to receive fuel from thegas-operated fuel pump when the delivery pressureof the pump tends toexceed a predetermined pressure, the accumulator being arranged tosupply accumulated fuelto the injector means.

The present invention has for a subsidiary object to provide a fuelinjection system for ahigh compression pressure engine in which therelation between the timing at full load and when idling can be variedin an appropriate manner.

According to a subsidiary feature of the present invention, therefore, ahigh compression pressure engine has a gas-operated fuel injection pumpcomprising a pump piston operating ;in a pump cylinder, the gas pressurefrom the combustion chamber of the engine cylinder beingapplied to oneside of the said pump piston, and means being provided for applying tothe other side of the pump piston a gas pressure which increases as thesupercharge pressure increases. This gas pressure may be derived from asuitable part of the engine, or machine driven thereby,

such that the delivery pressure of the fuel pump at ,full

load is reduced in comparison withthat whenidling. The said part may forexample be the cushion cylinder or'the engine case in a gas-generator,or the scavengepressure in adiesel. When the .said part is the cushioncylinder the maximum cushion pressure is preferably employed. The effectis thus to retard the injection at full load, whereas little effect isproduced at no load, and hence a relative change in timing between fullload and no load is produced in the required sense.

The invention will be described, by way of example, with reference tothe accompanying drawings in which-- Fig. 1 shows somewhatdiagrammatically and input a preferred form that the fuel pump andaccumu lator according to the invention may take,

Fig. 2 is a. diagram showing the combination of components of Fig.1 inan engine, 'Fig. 3 shows a modified form of the fuel pump and Fig. 4shows a modified form of the accumulator. '{Referring to Figs. 1 and 2,a fuel pump comprises a casing 11 having its upper portion formed as acylinder '12 in which works a piston 13. The upper end of the 'cylinder12 is connected by a pipe 14, as shown in Fig. 2,

to a diesel cylinder 15. The piston 13 has a piston rod 16' connectedthereto and the lower end of the piston rod constitutes a plungerworking in a cylinder 17. The piston 13 is biased upwards by a spring 24engaging a -member 25 fixed to the piston rod 16.

Fuel enters the pump through a pipe 18 and passes into the cylinder 17through an inlet valve 19 and a port 20.

-Fuel is forced out of the cylinder 17 by the pump plunger 16 through anoutlet port 21 and a spring-loaded nonreturn valve 22 into an outletpipe 23.

- The inlet valve 19 controls the quantity of fuel ejected from the pumpat each stroke of the piston assembly 13,

16 in the following way. The valve 19 is biased to its closed positionby a spring 26 and the upper end of its stem is acted upon by a cam 27forming one arm of a bell-crank lever rockably mounted upon an eccentricfulcrum 28. The other arm of the lever has a slot in which engages a pin29 fixed to the piston rod 16. The movements of the cam 27 produced bythe reciprocation of the piston assembly 13, 16- serve to open and closethe valve 19. The closing of the inlet valve is delayed by an amountwhich is variable by means of a lever 30 which rotates the eccentricfulcrum 28, thereby controlling the quantity of fuel ejected.

Gas pressure from a suitable part of the engine or itsassociated'equipment is applied through a pipe 31 to the underside ofthe piston 13. The point from which this gas pressure is derived can bechosen according to circumstances but must be such that its value ishigher at gas pressure applied at 31 is derived from the cushion of a.free-piston engine and that the maximum cushion pressure is to be used.For this purpose a non-return valve 32 is provided between the pipe 31and the interior of the casing 11. In this way a steady pressureapproximately equal to the maximum cushion pressure is applied to theunder side of the piston 13. A small leak 33 is also provided around thenon-return valve 32 in order to allow the pressure applied to the piston13 to drop when the cushion pressure drops.

As shown in Fig. 2, the fuel from the pump 10 passes through the outletpipe 23 to an accumulator 34 and thence by a pipe 35 to an injector 36.

The accumulator 34 'as shown in Fig. 1, comprises a piston 37 within acylinder 38, the upper face of the piston 37 being loaded by compressedair from any convenient source applied through a pipe 39. The undersideof the piston 37 is open to the atmosphere through a vent 40. The piston37 bears upon the upper end of a plunger 41 on a cylinder 42 incommunication with the fuel pipe through a port 43 in the side of thecylinder 42 and through a non-return valve 44 in the bottom of thecylinder 42. Downward movement of the plunger 41 is limited by thecushioning effect of the fuel trapped beyond the port 43 before itreaches the surface 45.

In operation, when the delivery pressure of the fuel .pump' 10 actingupon the underside of the plunger 41 tends to exceed the pressureapplied through the pipe 39 multiplied by the square of the ratio of thediameter of the piston 37 to that of theplunger 41, the plunger risesand fuel is received in the cylinder 42. When the force exerted upon theupper end of the plunger 41 by the piston 37 is greater than thatexerted upon the lower end by the fuel pressure the plunger 41 fallsthereby delivering fuel to the injector. The end of injection will occurwhen the plunger 41 over-rides the port 43, provided that the plunger 16of the injection pump 10 has at this time completed its downward stroke.

The passage including the non-return valve 44 is provided to allow fuelto enter the cylinder 42 as rapidly as is required, even when theplunger 41 has over-run the port 43, and to prevent fuel from leavingthe cylinder 42 excepting through the port 43, thereby providing ahydraulic buffer for the accumulator plunger.

Instead of loading the piston of the accumulator by means ofairpressure, as described, it may be loaded by means of fuel oil underpressure derived from the injection system through a non-return valveand a slow leak. The pressure required when starting the engine may thenbe provided by a single stroke pump plunger driven by the compressed airused for starting the engine. Air pressure would not then be 48. Theupper face of the piston 47 is open to the atmosphere through vents 49.It is assumed in this example that the pressure applied to the lowerface of the piston 47 is not the maximum cushion pressure but some otherpressure such as the average cushion pressure, the engine-case pressure,or a control pressure derived from the speed governor of the associatedturbine. Thus the non-return valve 32 and restricted passage 33 is notrequired and has been omitted from Fig. 3.

The control of the accumulator piston 37 may be effected as disclosed inthe specification of British Patent No. 628,132. Thus as shown in Fig.4, instead of the dash-pot arrangement, the under face of the plunger 41is in direct communication with the fuel pipe 23 and a spring butter,such as a pile of Belleville washers 50, and a shoulder 51 acting as astop are provided to limit the downward movement of the piston 37. Thespring buffer 50 prevents impacts of the piston 37 against the stop 51.

' I claim:

1. A high-compression supercharged internal combustion engine, fuelinjector means for said engine, a fuel pump having a piston operating ina cylinder, means coupling the combustion chamber of said engine to saidcylinder at one side of said piston to apply gas pressure to operatesaid piston, a pressure source yielding a pressure which increases assaid supercharge pressure in creases, means connecting said cylinder onthe other side of said piston to said pressure source, fuel feed meansconnecting said pump to said fuel injector means, and a fuel accumulatorin said fuel feed means, said accumulator having means responsive to apressure exceeding a predetermined pressure to admit fuel from said fuelpump to said accumulator.

2. An engine according to claim 1, wherein said accumulator comprises aplunger operating in a plunger cylinder, means applying pressure to saidplunger cylinder on one side of said plunger to urge said plunger in onedirection, and a port in said plunger cylinder on the other side of saidplunger connecting with said fuel feed means and applying fuel pressureto urge said plunger in the other direction, said port being positionedto be closed by said plunger.

3. An engine according to claim 2, comprising a nonreturn valve in saidplunger cylinder on said other side of said plunger connecting saidplunger cylinder with said fuel feed means and admitting fuel to saidplunger cylinder.

4. A high-compression supercharged internal combustion engine, fuelinjector means for said engine, a fuel pump having a piston operating ina cylinder, means coupling the combustion chamber of said engine to saidcylinder on one side of said piston, a pressure source yielding apressure which increases as said supercharge pressure increases, meansconnecting said cylinder on the other side of said piston to saidpressure source, and fuel feed means connecting said fuel pump to saidfuel injector means.

5. An engine according to claim 4, wherein said piston is a steppedpiston, the said one side thereof being the smaller.

References Cited in the file of this patent UNITED STATES PATENTS2,246,701 Steiner June 24, 1941

